Allow me to play devils advocate on the exhaust. An exposed on the side exhaust system will be very costly, both to you and the consumer. If its exposed it has to have perfect welds and be really shiney. A second cat will add a couple hundred too. Final thought on the matter would be that the majority of the solstice modding community already have aftermarket exhausts and you would have to prove to them that its worth it for them to throw out their old ones for your new one.
OK all that crap out of the way. I love the idea and concept. I think you should make one for your car. While I dont think it will be profitable for you to make production runs of them you may be able to do them by order.
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Victoria
2007 GXP Manual.